Odpowiedź
[tex]\displaystyle{ S = 20, \:\:\: g = 10}\\\\\displaystyle{ S = \frac { \: g t^2 \: } {2} }\\\\\displaystyle{ t^2 = \frac { \: 2 \cdot S \: } {g} = \frac { \: 2 \cdot 20 \: } {10} = \frac { \: 40 \: } {10} \:= \: 4 }\\\\\boxed{\displaystyle{ \:\: t \: = \: 2 \, \text{s} \:\: }}[/tex]
[tex]v = g \cdot t = 10 \cdot 2\\\\\boxed{ \:\: v \: = \: 20 \, \text{m/s} \:\: }[/tex]